1. Field of the Invention
The present invention relates to a map information displaying apparatus in a navigation apparatus for displaying: a route for a travel of a movable body such as a vehicle or the like; a name of a famous place or building at the vicinity of the route; and the like, together with a map to thereby support the travel of the movable body, and particularly relates to the map information displaying apparatus for displaying a so-called "bird's-eye view" as the map. The present invention also relates to a program storage device readable by the navigation apparatus to execute the program for displaying the bird's-eye view.
2. Description of the Related Art
As a position measuring apparatus for various movable bodies, such as a vehicle, an airplane, a ship and the like, there is a navigation apparatus, which superimposes a position mark (index) indicative of a present position, at which a movable body is presently located, on a point of a map corresponding to the present position and displays it, so as to perform a route guidance to a destination based on the position mark. In an on-vehicle type navigation apparatus among the navigation apparatuses, there are roughly a self-sustained type (i.e. a built-in type) navigation apparatus and a GPS (Global Positioning System) type navigation apparatus.
The self-sustained type navigation apparatus obtains a travel direction and a travel distance of the movable body by using built-in type sensors, such as a velocity sensor, an angular velocity sensor and the like, equipped in the movable body, sequentially integrates them with respect to a standard point so as to calculate a present position, and displays a position mark and a corresponding map on a display screen based on the calculated present position.
The GPS type navigation apparatus receives measurement radio waves from a plurality of GPS satellites launched in the outer space by using GPS receivers, calculates a present position of the movable body by using a three-dimensional survey or a two-dimensional survey based on the received radio waves, and then displays a position mark and a corresponding map on the display screen based on the calculated present position.
There is also a so-called hybrid type navigation apparatus, in which both functions of the self-sustained type and the GPS type are integrated.
Moreover, according to the on-vehicle type navigation apparatus, a route, on which the vehicle is scheduled to proceed, may be superimposed on the map and is displayed together with a famous place or building along the route.
According to the above explained on-vehicle type navigation apparatuses, a user (driver) can grasp the correlation between his present position and the map. Thus, even in an area to which he has never been, he can reach his destination without being misguided.
On the other hand, as for the map display in the on-vehicle type navigation apparatus, there is a map display by using a so- called bird's-eye view, in order to mainly enlarge a range which can be simultaneously displayed and perform a realistic map display.
The map display using the bird's-eye view is intended to display a map, for example, in such a way that a road map is obliquely overlooked from a sky (i.e., a one-point perspective projection view is displayed in which a topography corresponding to a map is seen from one point in the sky). For example, the bird's-eye view is used in a flight simulator and the like.
This bird's-eye view display is schematically explained with reference to FIGS. 13 and 14.
In FIG. 13, a plane M shows a map, and a rectangle abcd shows a display range of a display device for displaying a map. Then, when a view point is set to a position as shown in FIG. 13, a map range which can be seen through the rectangle abcd from this view point is a trapezoid ABCD on the plane M in FIG. 13. Namely, a map having a range much larger than that of the rectangle abcd can be seen from the position of the view point. Therefore, it is the bird's-eye view display to display an image on the display device, as if seeing the trapezoid ABCD of FIG. 13 from the position of the view point of FIG. 13. More concrete explanation is done here with reference to FIG. 14.
FIG. 14 shows an example, in which a road map at the vicinity of a route from a present position of a vehicle to a destination is displayed on the display device by using the bird's-eye view. In FIG. 14, the view point is set in the sky in a direction opposite to the destination with respect to the present position as a standard, and then a direction for the destination is overlooked from the view point. When the view point is set at such a position, an image is displayed in which a reduction scale of the map is gradually increased in conjunction with the approach to the present position from the destination as shown in FIG. 14. Namely, the periphery of the present position is magnified, and the route can be displayed over a wide range up to a place near the destination as compared with a case in which the map is flatly seen.
By use of the above explained bird's-eye view display, it is possible to display at one time the range much wider than that of the case in which the map is flatly displayed, and also possible to perform the realistic map display closer to an actual driving circumstance.
In the aforementioned on-vehicle type navigation apparatus, a name of a famous building and a name of a crossing may be displayed in addition to the road on the map at respective points corresponding to the building and the crossing respectively. However, in a case that these names and the like are displayed when the map is displayed by the bird's-eye view, characters indicative of the names and the like are displayed in a flat shape (in other words, in a two-dimensional display) as shown in FIG. 15.
However, if the characters are displayed in the flat shape on the map displayed by the bird's-eye view, although the map and the name can be displayed without any problem in the area close to the present position, since the reduction scale is lowered in the area farther from the present position, flat-shaped characters located at the places adjacent to each other may be overlapped with each other in the area far away from the present position. Hence, in that case, it is necessary to reduce a number of the characters of the names displayed in the area far away from the present position. This results in a problem that an essential function as the map is lost.